To track the location of a mobile device or a user having mobility (hereafter referred to as the “mobile user”) or predict the moving direction thereof, existing studies and conventional technologies utilize location information. Most technologies input grid location information, the location information of a base station or the like into a mathematical model, analyze a location, and then predict future mobility. Furthermore, using a centralized analysis method, a central system collects individual pieces of location information, performs analysis and prediction, and then provides the results of the analysis and the prediction to a corresponding base station or a mobile user as required.
The above conventional method has the following problems. First, the location information of a mobile user is a massive amount of data. To analyze and predict a location using such a massive amount of data, a considerably lengthy analysis processing time is required. Accordingly, it may be difficult to rapidly determine a location, and a real-time service designed to predict a location and transfer the results of the prediction may suffer from delay. Second, to analyze and store a massive amount of location information, required storage capacity and processing costs increase. Third, in the case of a centralized method, a large amount of data traffic is incurred, so that high data transmission and reception costs and traffic overload are incurred.
In response to this, Korean Patent No. 10-0969465 entitled “Method of Measuring Location of Mobile Node on Wireless Sensor Network” discloses an example of a method in which each node calculates a relative location using a distributed measurement/analysis method, rather than a centralized measurement/analysis method.
This prior art uses a distributed measurement/analysis method in a wireless sensor network. The prior art measures a location using the strength of a signal received from a reference node, that is, a reference for location, time of arrival (TOA), time of flight (TOF), time difference of arrival (TDOA), angle of arrival (AoA), etc., and a weight for each reference node is assigned based on the number of reference nodes and a virtual measured distance, thereby making initially set virtual location information accurate.
Although this method can accurately measure the location of each sensor node, it is problematic in that it cannot be easily applied to a network including mobile sensor nodes because an excessively long time is required due to the iterations of the process of acquiring the accurate location of each sensor node, etc.
Meanwhile, Korean Patent No. 10-1136375 entitled “Method and Apparatus for setting up Routing Path in Multi-hop Network” discloses a routing technology for acquiring minimum location-related information required for decision making, such as routing, etc., rather than acquiring accurate location information, unlike the above-described prior art, and attempting to avoid a failure element. This prior art presents a technology that determines a path along which a communication failure is expected to occur based on the mobile characteristics of a communication failure element and adaptively sets up a stable routing path.
This prior art proposes a technology in which a node that determines that there is a communication failure transmits a message providing notification of the communication failure to neighboring nodes within a predetermined hop count range and each of the neighboring nodes that has received the message providing notification of the communication failure acquires the mobile characteristics of a communication failure element based on the notification message and sets up a routing path again based on the mobile characteristics of the communication failure element. In this case, each sensor node does not determine the accurate location of the communication failure element, but each sensor node determines whether it is located with a communication failure range related to the communication failure element (that is, whether it is suffering from a communication failure) first and then notifies adjacent nodes of the results of the determination via a message. Other nodes may acquire the range of influence of the communication failure element and the possibility of approach of the communication failure element based on the notification message from the node suffering from the communication failure (a failed node) and a hop count with respect to the failed node.
Although this prior art is an effective technology that rapidly acquires only location information required for routing (that is, the range of influence of a communication failure element and the possibility of approach thereof, rather than accurate location information) and attempts to achieve successful routing, it has the following disadvantages. First, adjacent nodes cannot accurately determine location relationships with a communication failure element but can determine only hop counts because this conventional technology is based on a multi-hop network. Second, it is difficult to prepare for the influence of a communication failure element because location information can be acquired only from nodes that have been suffering from a communication failure element.
As a result, there is a need for the development of a distributed location measurement method that is more efficient than the above-described conventional technologies.